1. Field of the Invention
The invention relates to packing members which may be in either annular form or in strip form and which are used to seal between two elements of an assembly which may be stationary or relatively moving. They may be used to seal between two relatively rotating elements, such as a rotating shaft and stuffing box or a stationary shaft and rotor, or between two relatively reciprocating elements such as a piston and cylinder. In any case they provide a pressure seal against the flow of a fluid between the two members. The individual packing members may be used singly in some applications and may be stacked in other applications.
2. Description of the Prior Art
One type of packing previously used in the above discussed applications is generally V-shaped in cross-sectional configuration. It has a head or top which corresponds to the apex of the V and two lips extending radially and axially away from the head to form the legs of the V. The pressure of the fluid being sealed against forces the lips apart so that one lip seals against one of the elements of the assembly and the other lip seals against the other element. One of the disadvantages of this type of packing is that adapter rings are needed at the top and bottom of a packing member, or at the top of an uppermost and the bottom of a lowermost packing member in a stack, to keep the packing members properly positioned. Not only do these adapter rings make the sealing system more complicated and expensive, but due to the additional space they consume, it is often impossible to use the system because there is not enough space for a packing member plus the adapter rings or because there is not enough room for the adapter rings plus the number of packing members needed in a stack to provide a sufficient seal for the particular application.
One improvement over this type of packing is known as a "modified V" type packing. This type still has a head and a pair of lips extending therefrom. However, the bottom of the packing includes a pedestal extending away from the head in the general direction of the lips and centrally located therebetween. The pedestal provides support so that the bottom adapter ring may be eliminated. However, the top adapter ring is still needed. Moreover, the lips are adjoined to the pedestal by relatively thin portions which reduce the wear zone. The packing tends to fracture at these thin portions particularly if it is formed of a fabric impregnated with an elastomeric, thermosetting, or thermoplastic material.
The above-mentioned U.S. application Ser. No. 444,331, now U.S. Pat. No. 3,915,463, discloses a strip or annular packing member which eliminates the need for both top and bottom adapter rings and maximizes the wear zone of the packing.
The packing member of U.S. application Ser. No. 444,331, now U.S. Pat. No. 3,915,463 includes a head having a relatively broad planar head surface and first and second lip sections. Each lip section has a laterally outwardly facing side surface and a base. A groove between the bases extends along the length, or circumference, of the packing member opening downwardly away from the head. At least one of the lip sections has a cavity extending along the length or circumference of the packing member between its side surface and the groove and also opening downwardly. The cavity forms a pressure trap and preferably its laterally outermost surface extends laterally outwardly from top to bottom. Two such cavities may be provided, one in each lip section. These cavities are preferably not as deep as the groove.
The relatively broad planar head surface of the head of the packing member eliminates the need for a top adapter ring. Furthermore, the provision of two bases, spaced apart by the groove, provides a relatively broad support region at the bottom which eliminates the need for a bottom adapter ring. Sealing ability, however, is not sacrificed. Pressure entering the cavity aids in achieving low pressure sealing by urging the lower portion of the side surface laterally outwardly. Thus, the side surfaces are forced into sealing engagement with the faces of the members being sealed by the pressure sealed against.
A wear zone or heel is provided on the side of each lip section adjacent the broad head surface of the head. The lip sections flex laterally inwardly relatively easily upon insertion of the packing member into the assembly to provide an initial seal without application of pressure. When high pressure is applied, it fills the groove bringing the wear zones into tight contact with the adjacent faces of the assembly. Thus, high pressure wear will occur primarily at the wear zones. These wear zones are maximized by the thickness of the lip sections. Thus, considerable wear can occur without danger of the lip sections breaking or a seal being lost.